1. Field of the Invention
The present invention relates to a manufacturing method of a diffraction grating.
2. Description of the Related Art
A Blazed diffraction grating has a grating pattern having a sawtooth sectional shape, and each grating has a Blazed surface that receives incident light most and a counter surface neighboring the Blazed surface. It is important for a good optical characteristic to precisely form the Blazed surface that receives the incident light most. Japanese Patent Laid-Open No. 2010-286829 proposes cutting processing so as to simultaneously form both a Blazed surface of a certain grating and a counter surface of a neighboring grating.
Assume that each grating groove is formed by two-stage cutting processing so as to form the Blazed surface with higher surface accuracy. In this case, the first cutting processing provides cutting processing to a work using two blades of a cutting tool by moving the cutting tool. Next, the blade of the cutting tool used to form the counter surface is slightly moved towards the grating plane side along the cutting surface. The second cutting processing provides cutting processing at that position by moving the cutting tool. However, this two-stage cutting processing is likely to cause burrs or surface roughness.